(1) Field of the Invention
The present invention relates to line pressure control apparatus and method for a vehicle which are capable of producing a line pressure which is a basic pressure of a controlled hydraulic pressure for a predetermined hydraulic pressure engagement frictional elements based on discharge pressures from two oil pumps.
(2) Description of Related Art
In a hybrid vehicle constituted by a hybrid drive train in which an engine, a first clutch, a motor•generator, and a second clutch (automatic transmission) and driving wheels are serially connected in this order, the first and second clutches are hydraulic pressure clutches whose engagement and release are controlled by means of working oil (or hydraulic oil). In such a hybrid vehicle as described above, in an EV mode in which the engine is stopped and the vehicle is traveling only with the motor•generator as a power source, the first clutch is released and, in a HEV mode in which the vehicle is traveling with the engine and the motor•generator as power sources, the first clutch is engaged (for example, refer to a Japanese Patent Application Publication No. (tokkai) 2007-015679 published on Jan. 25, 2007 (which corresponds to a United States Patent Application Publication US2006/0272869 A1 (published on Dec. 7, 2006)).
In the above-described hybrid vehicle, at a time of the HEV traveling mode or EV traveling mode, a discharge pressure from an oil pump (hereinafter, referred to as a mechanical oil pump M-O/P) rotationally driven by means of an input shaft of a transmission is used to control a line pressure. In addition, during a vehicle stop or during a vehicle start region, the discharge pressure from an electrically driven oil pump driven by an electrically operated motor is used to control the line pressure. The electrically operated motor is used to supply the hydraulic pressure to the first clutch (a normal close type) and second clutch.